Derivative instruments - (Hedged Liabilities and Cumulative Amount) (Details) (Details) - USD ($) $ in Millions |
Dec. 31, 2019 |
Dec. 31, 2018 |
|---|---|---|
| Derivative [Line Items] | ||
| Cumulative amounts of fair value hedging adjustments related to the carrying amounts of the hedged liabilities | $ 296 | $ (53) |
| Current portion of long-term debt | ||
| Derivative [Line Items] | ||
| Carrying amounts of hedged liabilities | 903 | 2,396 |
| Cumulative amounts of fair value hedging adjustments related to the carrying amounts of the hedged liabilities | 4 | (3) |
| Carrying value with discontinued hedging relationships | 1,000 | |
| Hedging adjustments on discontinued hedging relationships | 3 | |
| Long-term debt | ||
| Derivative [Line Items] | ||
| Carrying amounts of hedged liabilities | 8,814 | 9,361 |
| Cumulative amounts of fair value hedging adjustments related to the carrying amounts of the hedged liabilities | 292 | (50) |
| Carrying value with discontinued hedging relationships | 136 | 137 |
| Hedging adjustments on discontinued hedging relationships | $ 36 | $ 37 |